It might be noticed by some who really want to do a good job on their
reproducing grand, that the soft pedal action is very important to establish a
sensitive, perfectly adjusted nuance between soft intensities without creating
a threshold pressure on the damper levers which would lighten them enough to
allow some notes to ring through. (Most prevalent in the bass and lower
tenor).

When observing the hammer lift rail on a grand action, one will notice that
especially on reproducing grands, this rail is often uneven, or some would
say, "warped," not knowing, of course, that the "warpage" was usually
purposeful, and placed there by the regulator. As a necessary caveat, this
purposeful angle of the hammer lift rail does cause the wood to bend over
time, appearing to be "warped." It's all initially in the settings of the
swivel hooks.

Certainly, it was never caused by hammer weight! How can we say that
absolutely, without any equivocation at all? Because no grand action or player
grand can even be regulated by initially resting the hammer shanks on the
rail! As time went on and felts compressed and buckskin knuckles dented, the
shanks went down a tad, of course. In some cases they went down all the way to
the felt on the "rest" rail. Then what happened? As soon as the rail took the
tiniest small fraction of the weight (maybe a gram or a half a gram), the
hammer stopped sinking and everything from that point was in equilibrium,
fully supported again by the now-compressed buckskin and felt. If you don't
believe that, remove the rest rail, and you'll see that the hammers are
resting exactly where the rail was. That is called "equilibrium," or zero
force. So it doesn't matter how heavy the hammers are. If you have regulated
them initially, they are at least 1/8" above the hammer lift rail (in the
treble, and more in the bass) at that time. That's a whale of a lot of
compression to go through before they even begin to touch the felt of the lift
rail. (That's roughly the rule. I cover the exceptions below)

One way to show whether or not a crooked lift rail was intentional is to look
at the factory felt blocks under it. It was always supported by these fixed
risers and its initial angle will be determined by this. A second way to show
that the angle of the hammer rest rail may be part of the piano's regulation
is to disassemble it and notice that the swivel hooks which hang the rail are
often bent at the factory. Were you to straighten them all out and screw them
back in at exactly the same depth, you would sometimes have a real mess unless
you knew how to do it.

Most lift rails you will find tend to favor the bass side over the treble. In
other words, they are purposely bent to tend to lift the bass first. If hammer
weight were the culprit, that angle would be reversed, of course. But there
are pianos in which one will find a straight lift rail, or even a rail that
tends to lift the treble before the bass. Why would they do that?

The answer is, "regulation." In many player grands, the damper levers are
helped by damper lever springs, which have been added. In some, the springs
are only on the bass dampers. In others, the springs go all the way up. Those
springs are counterbalanced for key tail weight, for when the hammer rail
lifts and the key touches the damper lever, the damper won't lighten any more
than its lead weighting requires. Otherwise, you may have a few dampers
allowing their strings to sing through when the lift rail is actuated.

The factory knew their piano's characteristics that way, and also understood
that if they were to lift the hammers in a straight line, they would have
damper problems, so they purposely "skewed" the hammer rail lift for this
purpose, too.

When you find a "warped" hammer rail, remember that in all likelihood it was
the factory who intended the hammers to lift that way for a very good reason.
Unless you are an expert at grand reproducing regulation, don't touch it.
Re-regulate your action by raising the shanks a bit above the rail again.
Granted, you will find many of these pianos whose shanks cannot be an even
distance from the rail. That is normal. Also, in grand regulation, straight
lines and mechanical exactitude from note to note may look pretty but is not
desired, anyway. Each note is to be regulated ultimately as a separate device,
once the general starting line has been established, and a finely regulated
action is not supposed to LOOK precision with all its neighboring notes. It is
supposed to PLAY with precision. There is the difference.

The angle of the hammer lift rail is therefore dependent on basics like damper
lever weight, deflection compensation for lift rod placement, and other piano
hammer line and loudness characteristics. By propping up the lift rail and
playing the notes by hand, one is able to get a feel for what it should be set
to. When you hear strings ringing through their dampers this way, you know
that unless you can pull the damper lever stack and re-tension the springs,
then you will have to drop the height of the rail accordingly. Do not unlevel
the key tail damper felts with any more than thin paper inserts and call that
a "regulation." You will be causing more problems than you are solving.

Were you to drop the height of the hammer lift rail enough to stop this
ring-through on some grands, you wouldn't have enough lift at the extreme
other end of the piano to do any meaningful softening. Thus, you will quickly
understand why the factory compromised linear "perfection" and achieved
sufficient hammer rail lift to create a soft pedal effect.

Everything in correct piano action regulation is a compromise. You have to be
very familiar with actions and have had many years of experience with them
intimately to see exactly what are the most important parameters. Reproducing
grands must be regulated differently from ordinary grands, but the overall
regulation must feel almost exactly the same at the key. The height and angle
of the hammer lift rail is a "given," in most cases, and should not be
"adjusted" by someone who really doesn't understand the basics. So be happy
with your lift rail. It was adjusted that way for a very good reason!

If, however, your hammer rail shows evidence of bowing-- that means, sagging,
such that the lift line is catenary, you may opt to replace it for that
reason. So if that is the case, after removing the rail, wrap tape exactly at
the point the hook enters the rail, or mark it so you can get the same hook
back in exactly the same place it was taken from. Hardwood is best for this
rail, and the best hardwood is usually something like African straight-grain
mahogany or other hardwoods known for their ability to remain straight and
true. 95% of the time, all that will be needed is a little more support and
changes to the felt to true it up again. After that, the rail will again be
fully supported.

Yes, an expert can usually improve on it because these adjustments were done
quickly. But what is usually there is far better than a novice will ever get
it.